<!DOCTYPE HTML>
<style>
  div {
    position: absolute;
    top: 0;
    left: 0;
    width: 200px;
    height: 100px;
    background-color: red;
  }
</style>
<div></div>
<script>
  document.querySelector('div').animate(
    [
      { transform: 'rotate(0deg)' },
      { transform: 'rotate(360deg)' }
    ], {
      duration: 3000,
      iterations: Infinity
    }
  );
</script>
